Reclamation of used synthetic lubricating oils



2 1958 A. H. MATUSZAK EIAL 7,

RECLAMATIQN OF USED SYNTHETIC LUBRICATING OILS Filed Oct. 27, 1954 muhwwa Alfred H. Motuszak' James W. Hand, Jr.

Inventors John C. Monday By fzwzafi mtfomey United States Patent-O" RECLAMATION OFUSED SYNTHETIC LUBRICA'I'ING OILS Alfred H. Matuszak, Westfield; James W. Hand, In, Green. ll ge,- and Iohu- C- M n ay, C wf assignors to E'sso Research and Engineering Company,

' a corporation of Delaware Application October 27, 1954, Serial No. 465,118 4' (C This invention relates to a method for recovering valuable components of complex esters from oil compositions: containing such complex esters and more particularly relates to a methodjfon recovering the dibasic acid and glycol components of complex esters from synthetic lubricating oil compositions containing such complex esters.

In an eifort to obtain superior lubricating oils having specific and unusual characteristics, new synthetic lubricants have been developed; One class of material which has attracted unusual interest as synthetic lubricants are those materials which are known to the art as the complex esters. In, general. these syntheticlubricating oils are characterized, by higher Viscosity indices and. lower pour points than mineral oils. of corresponding viscosity. L bricant po s s ing s c p op s h e pe value in the lubrication of engines which are subjected. to. high temperatures. such as combustion turbine engines, particularly those of the prop-jet type. Mineral oil lubricants are generally less desirable for use in such engines because of their tendency toresult in a higher percentage of carbonaceous residue which accumulates on moving partsand interferes with the. operation of the engine. In addition, the relatively high pour points and lowflash points of such compositions are undesirable. The synthetic lubricants of the complex ester typeare especially adaptable to use under such conditions since these lubricantshave a desirable combination of high flash points, low pour points, and high viscosities, and eliminate or reduce, in a great number of applications, the necessity for additive agents. Generally these complex esters which are utilized in synthetic lubricant blends; for jet aircraft have the following'ranges ofproperties:

ASTM flash point 420mm ASTM pourpoint Below -.-.65 F. Kinematic via/210 F 9 to 11 cs. Kinematic vis./40 F 11,000 to 25,000

In, addition to the complex esters, commercially useful synthetic lubricants preferably contain diesters of dibasic acids and monohydric alcohols. It has been found that a synthetic lubricating oil base stock containing both complex esters and diesters is superior in many respectsto the individual stocks. Also, Commercial, synthetic lubricants may contain small amounts of additives such as tricresyl phosphate, phenothiazine, sulfonates, lecithin, sorbitan monooleate, and the like.

After synthetic lubricants have; been used for' some time in jet aircraft and the like, they become unacceptable for further use due tothe presence of contaminants such as water, low boiling hydrocarbons, acids, metals, metal salts, sludge, carbonaceous solids, and the like. Heretofore such used synthetic lubricants have been processed" to recover their diester content by distillation and the remainder of the synthetic lubricant, including the com plex ester, has been discarded, Thus the expensive cmponents of the complex esters, such as the glycol component and particularly the costly dibasic acid component;

have not been recovered heretofore. Due to the nonvolatile nature of the complex ester, the distillation process' employedto recover the volatile diester has not been feasible in commercial distillation, units. In addition to the complex esters which are discarded in used synthetic lubricants, there is also on occasion'a substantial amount of the complex esters discarded as a result of olf -spe cifi cation batches of: synthetic lubricants. Thus it is apparent that it would be highly desirableto have a process available which-could be utilized to recover the valuable components of'complex esters, particularly the expensive glycoi and dibasic acid-components, so asto thereby elin inate the discard of; such costly materials. a

A novel method has now been found for; recovering the glycol and dibasic acid components of complex esters from oil compositions, such asiusedor otf specifi'catign commercial synthetic lubricating oil compositions. The new method'involves the transesterification ofgthe cornplex ester" by a reaction between the complex ester and a monohydric alcohol whereby the dibasic' acid component is converted to a diesterandthe glycol: component is converted to free glycol. In general, the method of this inventioncomprises heating a mixture comprising the oil composition which contains the complex Lester, a monohydric alcohol, and an esterification catalyst until at least a portion of the complex ester is transesterified into a freeglycol product and a diester product and subsequently removing at least one of the products from the mixture. The met-bod of; this invention may. be utilized to recover such components from any complex ester containing at leastone dibasic acid residue and' at least one glycol residue. More specifically, the method of the presentinvention'm-ay be utilized to recover the glycol" and dibasic acid components from a complex ester having the following general formula:

A (glycol-dibasic t acid) where A is seIected fromthe group consisting o fjmon'o! basic acid 'residues and monohydric alcohol-dibasio'acid residues, B is selectedfrom the group consisting. of monohydric alcohol residues. and monobas ic acid-glycol residues, and: x is an integer of about 1 to16. It; will-be understood that-: where the complex esters are set forth in this specification in theforn of a; formula of the type shown above that it is implied that the various c0mp,o-

nents- (alcohols, glycols and acids) are joined together with the elimination ofwater as occurs in an esterifica' tion reaction. Such formulae are utilized in this specifi cation to simplify the description of'the complex esters;

The method of" this invention, wherein acomplex ester:

is reacted with amonohydric alcohol in the presence of an esterification catalyst, may be illustrated by the fqlf lowing equations involving a particular complexesterz Alcohol-acid -glycol-acid-) alcohoH-alcoholg alcohol-acid-alcohol-l- (glycol-acid) alco hol (Glycol-acid alcohol-i-alcohola. alcohol-acidaalcohol+glycol+ glycol-acid ialtohol- (:2);

(Glycol-acid) alcohol+alco h ol@ alcohol-acid.-al cohol+( glycol-acid) glycol;-

(Glycol-acid) -glycol+.alcohol t Y (ac-2 alcohol-acid-alcohol+ x-l glycol;

equation:

Alcohol-acid- (glycol-acid) -alcjohol -lnalcohol (x+ l) alcohol-acid-alcohol-{-xglycol+unreactcd alcohol In general, it is preferred to utililze 'a sufiicient'atnount Patented Oct. 21,1958

to v

; '("4:): The desired overall reaction is shown by, diet-following;

'dues, and x is an integer of about 1 to 6.

vert all of the dibasic acid components to diesters is utilized in order to assure substantial completion of the transesterification reaction. It will be understood that the method of this invention is applicable to complex esters other than the particular type shown in the above equations.

Generally,.synthetic lubricant compositions will contain a combination of a complex ester and a diester. The method of this invention may be utilized to recover complex ester components from such compositions or other oil compositions containing as little as about 1% by volume of complex ester. In general, if the oil composition contains less than about by volume of the complexfester, it is preferred to initially remove the original diester by distillation prior to carrying out the transesterification reaction with the complex ester. When the proportion of complex ester is greater than about, 10% by volume, the original diester may be similarly removed by distillation prior to the transesterification reaction, although it is generally preferred to carry out the transesterification reaction of the complex ester first and then to separate the original diester along with the newly formed diester from the resultant reaction mixture. It has been found that higher recoveries are obtained by carrying out the transesterification reaction of the complex ester in the presence of the original diester in such instances. Preferably the monohydric alcohol utilized in the transesterification reaction corresponds to the monohydric alcohol residue of the original diester contained in the synthetic lubricating oil compositions since this simplifies the recovery of the diesters. The glycol recovered by the method of this invention may be utilized, for example, in the preparation of new complex esters which may then be used to prepare new synthetic lubricating oil compositions. The diester formed in the transesterification reaction may be used, for example, as the diester component of new synthetic lubricating oils, as a plasticizer, etc. The method of this invention may be carried out by a batch or continuous procedure.

As has been stated, the method of this invention may be utilized to recover the glycol and dibasic acid components of any complex ester containing at least one glycol residue or radical and at least one dibasic acid residue or radical. Generally, the complex esters which are utilized commercially in synthetic lubricant compositions and which may be reclaimed in the method of this invention have the following general formula:

A-(glycol-dibasic acid) -B l where A is selected from the group consisting of monobasic acid residues and monohydric alcohol-dibasic acidv residues, B is selectedfrom the group consisting of monohydric alcohol residues and monobasic acid-glycol resi- In general, the complex esters utilized in' synthetic lubricating oils are predominantly those where xequals 1, although during the preparation of such complex esters, higher molecular weight esters, such as those where x is in the range of A sample of the product being tested for acidity until the.

about 2 to6, arealso formed in lesser proportions. Also,

during the preparation of these complex esters, a certain I amount of diesters will normally be formed. Thus, the

overall product resulting from the preparation of complex esters will generally be a mixture of diesters. and complex esters of varying molecular weight.

The following five types of complex esters may be utilized in .themethodof this invention and thus their glycol and dibasic acid residues may be recovered as afree glycol product and as a diester product, respectively:

TYPE, I.-MONOBASIC ACID GLYCOL DIBASIC ACID-GLYCOL-MONOBASIC ACID This complex ester may be represented by the following structural formulaz.

' carrying out a straightforward esterification reaction. The

reaction conditions are continued with an occasional minimum acidity is attained.

TYPE II.---ALCOHOL-DIBASIC AClD-GLYCOL-DI- J BASIC ACID-ALCOHOL This material may be represented by the following formula:

R 00CR COO-R OOCR C0O R wherein R and R are the combining radicals of the alcohol, R and'R are the alkyl radicals of the dibasic acid, and R is the alkyl radical of the glycol.

These esters are prepared in the manner similar to those of Type I.

TYPE IlI.-ALCOHOL-DIBASIC ACID-GLYCOL' MONOBASIC ACID These esters are prepared by reacting a dibasic acid and a glycol under such conditions that one hydroxyl materials may be said to have the general formula:

R -0OCR COOR O0CR wherein R is the combining radical of the aliphatic aI-j cohol, R the alkyl radical of the dibasic acid, R the alkyl radical of the glycol, and R the alkyl radical of the monobasic acid.

The preparation of these ester materials is specifically set out in U. S. Patent No. 2,575,195.

TYPE IV.-ALCOHOL-DIBASIC 'ACID-GLYCOL-DI BASIC ACID ALCOHOL These materials may be said to have the general formula: Y

R OOCR COOR OOCR COO-R wherein R and R are the combining alkyl radicals of the alcohol, R and R the alkyl radicals of the dibasic acid, and R is the-alkyl radical of the glycol.

It will be noted that the esters of Type IV'have the same structural formula as Type II. However, these complex esters are prepared by reacting an alcohol with 1 a dibasic acid under such conditions that a half ester is formed and reacting two moles of such an ester with one mole of a glycol. The preparation of this type of synthetic ester lubricating, oil is set out in detail in copending application Serial No. 52,429, nowissued as U. S. Patent 2,703,811.

TYPE V.-MONOBASIC ACID-GLYCOL-DIBASIC' ACID-GLYCOL-MONOBASIC ACID These synthetic esters may be formula:

said to have the general wherein R and R are the alkyl radicals of the mono- 1 basic acid, R and R are the alkyl radicals of the glycol, and R is the alkyl radical of the dibasic acid.

It will be noted that these synthetic esters are the sameas those appearing above under Type 1 except that this type is prepared by reacting a monobasic acid with a glycol under such conditions that a half ester is formed and reacting two moles of such ester with one mole of a dibasic acid. The details of the preparation of this;

type of synthetic ester are set out in U. S. Patent No. 2,575,196.

As was set out above, these complex ester materials are prepared by- Fomb pation of an alcohol, amen -f Amyl alcohols 2-ethylbutyl alcohol n-Hexyl alcohol n-Octyl alcohol Zethylhexyl alcohol Nonyl alcohol Decyl alcohol C C C (2 0x0 alcohols weight olefinic materials are sometimes employed. The,

alcohols obtained in this manner normally have a branched chain structure.

The monobasic acids are those preferably having about 4 to 13 carbon atoms per molecule. However, other monobasic acids may be employed if desired; Among the mono'ba'sic acids which may be employed to prepare complex esters, the following alkanoic acids may be listed as illustrative:

Propionic acid Butyric acid 2-ethylbutyric acid Valerie acid Caproic acid Z-ethylhexoio acid Caprylic acid C8. OX0 acids C Oxo acids Laurie acid C Oxo acids Any of the corresponding thio acids The dibasic acids are those preferably having about 4 to 10 carbon atoms per molecule. However, other dibasic acids may be employed, if desired. Illustrative example of the dibasic acids which may be employed in the synthesis of the complex esters are the following alkanedioic acids.

\ Su'ccinic acid Adipic acid Pimelic acid Suberic acid Azelaic acid Sebacic acid Isosebacic acid T rimethyl adipic acid a Methyl adipic acid The glycols employed in preparing complex esters include ethylene glycol and any of the paratfinic homologues of the same containing up to 18 carbon atoms. These may include, for example, saturated glycols such as ethylene glycol, propylene glycol, butylene glycols, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, and the like. Since the glycols may also contain oxygen or sulfur atoms, -compounds such as diethylene glycol, tfiethylene glycol, the polyethylene gec'o'ls' of the formula: i

HO (CH2CH3O)',,CH3CH3OH where n is 1 to 2'6 and the polypropylene glycols of the general formula:

Br lib llil Ilia notmsnohcmonon where either R or R is a methyl group and the other is hydrogen, and where n is 1 to 20,; preferably 2 to 6, may likewise be employed. Glycols containing sulfur atoms in thioether linkages may also be employed, and these include compounds as thiodiglycol and 1,2-bis Q2- hydroxy-ethylmercapto) ethane. There also may beused glycols containing both oxygen and sulfur. in similar linkages; such a compound is bis-2(2-hy'droxyethoxy) ethyl sulfide.

When the complex esters described above are to be utilized as lubricants for .jet aircraft,: the reactants, i. e., the acids, alcoholsand glycols, will be selected and reacted together to formcomplex. esters having the properties (flash point, pour point, viscosity) set forth in detail heretofore; Generally, suchcomplex esters will coiit'ain' in the range of about 20 to carbon atoms per complex ester molecule.

It will be understood that the oil compositions from which the glycol and dibasic acid complex ester compo nents may be recovered in accordance withthemethod of this invention may contain other materials such as, for example, mineral lubricating oil basestock s. Also, used Oil compositions may contain water and hydrocarbon contaminants such as kerosene; naphtha, Iightga's oils and the like. The compositions may also include'dies te'rs such as those of the dibasic acids and monohydric alcohols described above. These diester'sm'ay actuallyrepresent in the range of about 0 to 99 b by volume ofth totallubricating oil composition. Also, the oil compositions may contain various conventional additives such as triciesyl phosphate, p'henothiazine', sulfonat'es, lecithin, sorh'itan niono'olea-te, pentaeryth'ritol monooleatc, poly a'crylates' and polymethacrylates;

The method of this invention comprises heating-'amixturecompris'i'ng 1) an oil composition containing the complex ester, (2) a rnonohydric alcohol, and (3) an esterification catalyst until at least a portion of the com? plex ester is transesterifie'd into a free glycol product and a' diester product and subsequently removing at least one of the products from the mixture. The monohydric' alcohols' which may be utilized in the transesterific'ation reaction are preferably those set forth heretofore as being useful for forming the complex esters. The alcohol used in the transesterification reaction may be the same as that used originally in the preparation of the complex ester" (when the complex ester contains a' 'riionohy'dric' alcohol residue). The alcohol which is utilized in the transesterification reaction may also be the same as that used originally in the preparationof the dieste'rbase stock (when i the oil composition contains such dieste'r cortiponerits')".'j Quite generally, it will be found that synthetic lubricant.

compositions will contain both complex esters and die'stejrs prepared from the same alcohol. Thus, particularly in the recovery of complex ester components from such compositions, it is preferred to utilize the same alcohol in the transester'ification reaction as was utilized in the preparation of the original base stock mixture of dies ter and complex ester. rowing the range of die'ster volatilities.

It is preferred to use in the transesterification reaction an amount of monohydric alcohol which will he sufi'ici'ent.

to react with all of the dibasic acid components ofithe complex ester to form" diesters as Well as to react with" any mon'obasic acid components to form simple esters. Generally, it is preferred to utilize an amount of alcohol in excess of the stoichiometric amount inorder to This facilitates the recovery by mi V amore rapid and complete transesterification reaction. In general, therefore, it is desirable to use at least about 2 moles of monohydric alcohol per dibasic acid unit and 1 mole of monohydric alcohol per monobasic acid unit in each mole of the complex ester. Amounts in excess of this, as much as 8 moles or more per dibasic acid residue, may be utilized if desired. With complex esters which are alcohol stoppered, that is complex esters which have alcohol residues at theextremities of the molecule, it is preferred in general to use at least 2 moles of alcohol per dibasic acid unit in eachcomplex ester molecule. Any excess alcohol remaining upon completion of the tranesterification reaction may be recovered by distillation from the reaction mixture and utilized for further transesterification reactions.

The esterification'catalyst utilized in the method of this invention may be any conventional esterification catalyst. Such catalysts are well known to the art and include the following:

Sulfuric acid Sodium hydrogen sulfate p-Toluene sulfonic acid Sulfosalicylic acid The amount of catalyst utilized in the reaction is preferably about 0.1 to 1% by weight, based on the total reactor charge. Y

The reaction is carried out at an elevated temperature such as a temperature in the range of about 70 to 300 C.; preferably a temperature in the range of about 150 to 250 C. is employed. The reaction is carried out for a period of time sufficient to convert at least a portion of the complex ester into a free glycol product and a diester product. Preferably the reaction is carried out until substantially all of the complex ester has been transesterified into the diester product and glycol product. The reaction time required to accomplish this will depend upon the batch size and will generally be in the range of about 0.5 to hours and preferably in the range of about 2 to 6 hours. In general, the method of this invention may be utilized to recover. complex ester com- 20 through conduit 22 and is passed through conduits 23, 24, 25, and 26 into reactor 40. A monohydrie alcoho], such as 2-ethylhexanol, is introduced into reactor 40 from storage tank 41 by opening valve 42 in conduit: 3-3. The monohydric alcohol enters reactor 40 through. conduits 43 and'44. Then an esterification catalyst, such as NaHSO is introduced into reactor 40 from hopper; 45 by opening valve 46 in conduit 47. The proportions: of reactants in reactor 40 are selected as described in detail heretofore. The reaction mixture comprising the used synthetic lubricating oil, the'monohydric alcohol and the esterification catalyst is heated to an elevated. temperature in reactor 40 by means of an electric heating coil or a heating coil 39 through which a heating medium, such as steam, like, is introduced and removed, respectively, through conduits 3% and 37. The reaction mixture in reactor .0 is preferably thoroughly mixed by means. such as by mixer 48 operated by motor 49. Any low boiling materials not removed overhead in tower 20 which are volatilized in reactor 40 may be removed from reactor 40 through vent line 50. The resultant transesterification ponents from oil compositions containing in the range of about 1% to about 100% by volume of complex esters.

The glycol and diester products formed in the tIansesterification reaction as well as any diester originally present in the original oil composition are preferably separated from the remainder of the composition by distillation at a reduced pressure in the range of about 0.01 to 10.0 mm. .Hg, preferably about 0.2 to 1.0 mm. Hg, to thereby avoid thermal, degradation of these materials.

The method of this invention will be more fully understood by reference to the single figure drawing which is a diagrammatic illustration of apparatus adapted to carry out the method of the present invention. ing, reference character 10 designates a storage tank containing a used synthetic lubricating oil composition containing atleast about 1% by volume of a complex ester such as di-Z-ethylhexanol-sebacic acid-tetraethylene glycolsebacic acid-di-Z-ethylhexanol. The remainder of the synthetic lubricating oil base stock comprises a diester such as di-2-ethylhexyl sebacate or C 0110 azelate. Valves 11 and 12 in conduits 13 and 14, respectively, are then opened to pass the used synthetic lubricating oil composition into distillation tower 20 which may be. any conventional distillation tower adapted to remove water and'low boiling hydrocarbons such as kerosene, gas oils,

naphtha, and the like, overhead. The water and low. boiling hydrocarbons are impurities resulting from the utilization of the synthetic lubricating oil composition in jet aircraft and the like. The water and low boiling hydrocarbon impurities are removed overhead from tower 20, through'conduit 21. position. contained mineral lubricating oil base stocks, these oils will also be removed overhead from tower 20.

The remainder of the used synthetic lubricating oil composition is removed as a bottoms fraction from tower In this draw-' Also if the original oil comreaction is carried out in reactor 40 at the conditionsdescribedindetail heretofore. I

After thetransesterification reaction has progressed to 3 the desired point, the entire contents of reactor 40 arepassed to filter 52 through conduit 53 by opening valve 54. Filter 52 removes from the reaction mixture any solid material, such as catalyst, carbonaceous solids, and the like and may be a filter press, a blotter press, an r Oliver filter, a bed of clay or the like.

The filtered reaction products are thereafter passed, through conduits 55, 56, and 57 into distillation tower 7% by opening valve 58 in conduit 56. Tower is any conventional distillationtower adapted to take over: head through conduits 71 and 72 any unreacted mono hydric alcohol in the reaction mixture. Valve 73 .is opened to permit this mono-hydric alcohol to be removed overhead through conduits 71 and 72 through which the unreacted monohydric alcohol may be passed to storage. The remainder of the reaction mixture is then passed from the bottom of tower 70 through conduit 74 into distillation tower which may be any conventional distillation tower adapted to take overhead a glycol 1 through conduit 81. Thus in tower 80 the glycol formed in the transesterification reaction carried out in reactor 40 is separated as a substantially pure product from the reaction mixture. The remainder of the reaction products is then with drawn from the bottom of tower 80 through conduits 82 and 84 and is passed into distillation tower which; is any conventional distillation tower equipped'to take a diester product, such as di-Z-ethylhexyl sebacate, over head through conduit 91. Thus the overhead product of distillation tower 90 includes any original diester base. stock present in the synthetic lubricating oil composition contained in tank 10 as well as the diester product formed. in reactor 40 by the transesterification of the complex ester. Any complex ester which has not been transester'if fied into glycol and diester components may be withdrawn from the bottom of tower 90 through conduits: 92 and 93 by opening valve 96. It will thus be seen that the synthetic lubricating oil contained in tank,10 has been separated into a glycol component removed overhead from tower 80 and a diester component removed overhead through tower 90; also-any unreacted alcohol remaining after the transesterification reaction in reactor 40 has been recovered as an overhead stream from tower 70.

Rather than originally removing any Water and low. boiling hydrocarbon contaminants and/ or mineral lubri eating oil base stocks from the used synthetic lubricating; oil in tower 20, if desired these relatively low boiling materials may be removed after the trans'esterification reaction. This is accomplished by opening valves 11 Dow-Therm, mercury and the conduits 55 and 61 by opening valve 62 in conduit 61 closing valve 58- in line 56 such that the filtered products are introducedinto distillation tower 60. Tower 66 is any distillation tower adapt-ed totake water and volatile hydrocarbons overhead through conduit 63. In this manner,H it will be-seen thatthe low boiling hydrocarhon contaminants and/or mineral luhricating oilbase stocks may be removed after the transesterification reasses isc'oziiplete'd raction mixture may then be passed from the bottom df tow'r 60 successively to towers 70780, and90' for further' separation therefrom of alcohoi; g'l'ycoian'dj dister, respectively A lsto if de's if'd, thdris'ed syntheticfiubricating oil passing through line 23 from tower 20 may be passed to distillation tower 30 through conduits 31 and 32 by closvalve26' in conduit 24 and opening valve 33 inconduit 31. Distillation" tower 30 may be any conventional distillation unit adapted to take overhead through conduit 34 any original diester base stock contained in the us'd synthetic lubricating" en. The remainder er the used synthetic lubricating oil composition may then be passed from the bottoiii" or tower'to through conduits 3'5,

25, and 26 to' reactor .40; This particular method of operation is especially desirable when the used synthetic iiihricat ing' oil composition originally contains less than afloat l??? by volume of complex ester. In this manan,- the feed stock to reactor 4 0 maybe concentrated so that it contains a high proportion of the complex ester,

thereby simplifying the transesterificationreaction. This particulaimethod of operation is also useful when the angina dies t e r base stock' contained in the used syn-. thetic lubricating oil composition is not the same diester as that formedin reactor 40 in the transesterification rac'tionand spbsequently removed; overhead from distilfitioii rows 90 through oyerhead conduit 91. In this wy therfoie, it is possible to separately recover the different diesters. When distillation tower 30 is empra ed, it is preferable to also utilize distillation tower 20 to remove low boiling contaminants such as water and hydrocarbons. In this way, th e diesterproduct taken overhead through overhead conduit 34 through tower 30 is not contaminated with such low boiling materials. When operating thisfii'ariner, the filtered reaction prodnets from filten52 are by-passeda'round' distillation tower 60 since the low boilingcontaminants have previously been removedin distillation tower 20 a The method ofthis invention is readily adapted toa continuous process. For enampleythe following is a dc sgription of a preferred method of operation wherein it is desired to remove the original dieste'r' base stock from the used synthetic lubrieati-ng oil priorto-the transest'erification reaction; Used synthetic lubricating oil is continuously withdrawn from tank andcontinuously passed to distillation unit through conduits 13' and 14. Low boiling contaminants are" continuously removed overhead from tower 20 through overhead conduit 21. The rerha'inder of the used synthetic lubricating oil is continuously passed from the bottonrof tower 20 throughconduits'22, 23, 31, and 32 into tower 30. The original diester base stock is continuously removed overhead from'tower 30 through overhead conduit 34 and the remainder of the used synthetic lubricating oil base stock .is continuously passed from the bottom of tower 30"-t'.hrougli conduits 35, and 26 i'ntoreac'tbi 46.

. A large volume of reaction mixture is maintained in reactor- 40 and the portion of the used synthetic'lubricating oilpassing through conduit 26 into reactor 40, as well as the catalyst continuously flowing from hopper 45 and alcohol flowing through conduit 44; is introduced at such moved overhead from tower 70 is contiil'u a rate intoreactor 40 that the residence therebi iri reactor 40- willbe sufiicient to obtain the" desired" degree of transester'ification; A portion of the" re'actio'n mixtili'e iii-reactor 40 is continuously withd'r-awn therefronP through conduit 53 and is continuously filtered thrbugh'filter fl. The filtered reaction products are" thereafter passed thropgh conduits 55, 56, and 57 into distillation tower '70 from which unre-acted' alcohol is'taken overhead through conduit 71'. In this continuous method of operation, in is preferred to recycle the separated" unreacted alcohol through conduits 71, 75, and 44 back-tor'eactor4m This is accomplished by closing valve 73 in line =72 and opening valve 76 in conduit Make-up alcohol is suppliedtb reactor 40fromtank 41 through conduit 42 wherein iflis mixed with the separated alcohol in'conduit'- 44I v The reaction products from the bottom ofi tower 70 are passed continuously fromthe bottom' 'thereof rineugneen duit 74' to distillation tower sfliwhereg'lycol 'foriiied i' the transesterification reaction is continuously takeh ov can through overheadconduit 81. The bottoms fr'onidistillation tower 86, which contain the dieste'r" foi'rh'e'd 'in th'e tr ansesterificatiori reaction, may be continuously passed through conduits 82, 85', and 32 ba'clr' to distillation ower 30. This may be accomplished by closing valve 83 duit 84'and opening valve 86' in conduit 85;- In this manner, itwil1 be's'een that the; originaldiest'ei base" stock i-td gether with the die'ster'for med in the transest'erification reaction, is removed continuously overhead 'thro'u'glioverhead conduit 34 of tower 30"a'nd' any uh'feac'ted complex ester is recycled back to reactor 40.

As an alternative, thef'hottoihs from tower may be continuously passed through conduits 82'aiidi-84'into distillationtower 90 where thediester formed by nansesteri fication' is removed overhead continuously through overhead conduit 91/ This is accomplished by'clo'sing valve 86 in conduit and opening valve 83 inconduit-84i The bottoms from tower may be continuously discarded from the sysferh'by passing them through conduits 92 and 93 by opening valve 96 in conduit 93. As an alternative; the bottoms from tower 90 maybe passed through conduits 92, 94, and 26 back to reactor 4Q.- This-may be accomplished by closing valve 96 in conduit 93 and opening valve in conduit 94. In this manner, the bottoms from tower 90 which may contain a substantial proportion of complex ester may berecycled' bafcl'rto reactor for transesterification. Preferably, in this method of tion; a minor ortion of the" bottoms from tower 90- e continuously or intermittently discarded from th sy'sltehi through conduit 93 so as to purge the system of boilihg'liquid contaminants.- I V In cases where the used synthetic lubricatingoil contains more than about 10% by volume of complexester, it i preferable to carry out-theitransesterificatibn reaction in the presence of the diester base stock contained in the original used synthetic oil composition. This method niay be carried out continuously as follows; Used synthetic oil from tank 10 may be continuously passed through eon duits 13 and 14 to distillation tower 20 to remove there fromlow boiling contaminants. The bottom's'ir-om t'ower 23, 24, 25, and 26 into reactor40-.' Esterification catalyst and monohydric alcohol are; continuously passed intore-' actor 40 through conduits 47 and44, respectively; and the reaction product and the transe'sterificatiofi reaction in reactor 40 are continuouslyre'meved therefrom. The rate of introduction of reactants and catalyst isadjusted such that their residence time in reactor 49 is sufficient to give the desired degree of transesterification; V

The reaction products from reactor 40 are continuously passed through conduit 53 to filter 5'2 and the filter-ed reaction products are passed continuously through conduits 55, 56, and.57 to tower 70. The'urireactedalcohoI-re- 'oiislyf recycled to passe to actor reactor 40 and free make-up alcohol is 40 from 41.- The bottoms nomwwer to" are t ;continuously to tower 80 from which glycol is continuously removed overhead through overhead conduit 81. The bottoms from tower 80 are then passed from conduits 82 and 84 into tower 90 where the diesters, including both the original diester base stock and the diesters formed in as phenothiazine, high boiling glycols, tricresyl phosphate,

rust inhibitors, etc. It may be used as is or the contaminants may be removed by suitable processing such as alkali washing, charcoal or alumina treatment. The resulting diesters are useful as synthetic lubricant bases, chemical intermediates, or as plasticizers. By reacting the recovered diester with recovered glycol, complex esters suitable for use as blending agents may be prepared.

It will be apparent that the method of this invention will suggest other modifications to those skilled in the art and it will be understood that such modifications may be made Without departing from the spirit of the present invention.

The invention will be more fully understood by reference to thefollowing example. It is pointed out, however, that the example is given for the purpose of illustration only and is not to be construed as limiting the scope of the present invention in any way.

Example A used synthetic lubricating oil composition which had previously been used in actual flight service of a turboprop aircraftengine was employed in this example. The original synthetic lubricating oil composition had the following formulation:

ORIGINAL SYNTHETIC LUBRICATING OIL COMPOSITION Ingredient: Wt. percent Synthetic'oil base stock 1 99.0 Phenothiazine 1.0

Valuable components of this .used synthetic lubricating oil composition were reclaimed by five diiferent methods as follows.

Method I .To 250 g. of the used synthetic lubricating oil was added 250 g. of Z-ethylhexanol and 1.25 g. of NaHSO catalyst. The mixture was refluxed with stirring at 195 C. for 4 hours to convert the complex esters to di-2-ethylhexyl sebacate. which thereby removed the catalyst, then stripped free of unreacted alcohol at reduced pressure before finally removing glycol and the original and newly-formed diester. The distillation Was carried out to a final liquid temperature of 280 C. The lower boiling contaminants, such as water and low'boih'ng hydrocarbons, alcohol, and glycol were removed at a temperature below about 200 C. vapor temperature at a pressure of 0.5 mm. Hg. The diesters were removed at a temperature in the range of about 200 C. to 235 C. vapor temperature at a pressure of about 0.5 mm. Hg.-

Method II.To 250 g. of the used synthetic lubricating oil'was added 250 g. of 2-ethylhexanol. No NaHSO was added as a catalyst. This mixture was processed in an identical manner to the mixture of Method 1.

' Method IIL-Io 2 50 g. of the used synthetic lubricat- The mixture was filtered ing oil composition was added 1.25 g. of NaHSO No 2-ethylhexanol was added. This mixture was processed.

in an identical manner to the mixture of Method I.

Method IV.In this method, 250 g. of the used synthetic lubricating oil composition were processed by the. procedure set forth in Method I except in the absence of Z-ethylhexanol and in the absence of NaI-ISO catalyst. a

Method V.In this method, 126 g. of the bottoms of Method II were blended with 250 g. of Z-ethylhexandl and 1.25 g. of NaHSO This mixture was then processed V in a manner identical to that described in MethodL.

The following results were obtained by the above-dew scribed five different methods:

diester Weight of Weight of' Weight of Dlester Method Forerun Diester Bottom Yield (g s 1 (2 1 (2 e 1 Includes water, low boiling hydrocarbons, glycol, and alochol re-i i moved by distillation 200 O. 0.5 mm. Hg). 2 Diester removed by distillation (200-235 O. 0.5 mm. Hg). In-

eludes original diester base stock plus diester formed by transesterlflw' tron.

3 80.2% yield based on 126 gms. of starting material. a a

It will be noted that substantial increases in the yields of diester were obtained only in the case of the catalyzed- Z-ethylhexanol reactions (Method I and Method V) whichl were carried out in accordance with the method ofthepresent invention. Without catalyst and/or without ale.

cohol (Methods II, III, and IV) the normal diester yield was about 42%, but with the combination of catalyst and alcohol the diester yields were approximately'dou bled. With this type of used synthetic lubricating oil, which normally contains about 50 to 55% of complex esters, conversion in the presence of the original diester. (Method 1) gives a better yield than when the original. diester is first removed (Method V). It is believed that! diester solvency may be a factor contributing to difference.

What is claimed is: 1 f 1. A method for preparing a glycol and diester from a complex ester having the formula: i

A-(glycol-alkanedioic acid) ,,B

wherein A is selected from the group consisting of alkanoic acid residues and alkanol-alkanedioic acid residues,

catalyst, then separating said products from said mixture by distillation. l

2. A method according to claim 1 wherein said mixture initially also contains a diester of said alkanol and said alkanedioic acid.

3. A method for recovering a glycol and diester from a complex ester having the general formula:

Alkanol-alkanedioic acid-(glycolalkanedioic acid) -alkanol.

wherein said alkanol is a C5 to C alkanol, said'alkanez dioic acid is a C to C dicarboxylic-acid, said glycol is saturated and x is 1 to 6, said complex ester having ing oil qualities and containing a total e carbon atoms, said method comprising m:

complex ester with a C to C alkanol and an esterification catalyst, heating said mixture to an elevated temperature until a portion of said complex ester is esterified into a free glycol product and a diester product of said alkanedioic acid, removing said catalyst from said reaction mixture, then separating said products from said mixture by distillation.

4. A method for recovering glycol and diester from a synthetic lubricating oil composition wherein the synthetic oil base stock consists essentially of (A) a diester having the formula:

Alkanol-alkanedioic acid-alkanol and (B) a complex ester having the formula:

Alkanol-alkanedioic acid-(glycolalkanedioic acid) -alkanol wherein said alkanol is a C to C alkanol, said alkaneis esterified into a free glycol product and a diester prod uct of said alkanedioic acid, removing said catalyst from said reaction mixture, then separating said products from said mixture by distillation.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS 683,803

Great Britain Dec. 3, 1952 

1. A METHOD FOR PREPARING A GLYCOL AND DIESTER FROM A COMPLEX ESTER HAVING THE FORMULA: 